1. Field Of The Invention
The present invention relates to a short dwell coater apparatus for applying coating material to a web. More specifically, the present invention relates to a short dwell coater apparatus for supplying coating material to a web which is supported by a backing member.
2. Information Disclosure Statement
In the coating art, short dwell coaters have been used for applying coating material to the surface of a web as the web supported by a backing roll moves past the coater apparatus.
More specifically, short dwell coaters include a coater housing which defines a cavity connected to a source of pressurized coating material.
The cavity includes an application zone for the passage therepast of the web to be coated.
One advantage of the aforementioned short dwell coater is the short residence time of the web as the web moves past the application zone. The short residence time permits the application of coating material to the web while avoiding excessive penetration of the coating material into the surface of the web. Accordingly, only a very thin film of coating material is applied to the web, thereby reducing the amount of coating material required for a coating operation.
Additionally, due to the reduced penetration of coating material through the surface of the web, the strength of the resultant coated web is maintained so that web breakage is reduced.
However, in certain applications, it is desirable to increase the pressure at which coating material is applied to the web while avoiding the disadvantages of a prior art flooded nip coater in which a roll rotating through a pan of coating material applies coating material onto the sheet.
Additionally, when operating a short dwell coater above 3,000 feet per minute, streaking of the resultant coating has been a problem. Such streaking is caused by entrainment of air by the web as the web extends into and past the application zone. The air forms vortices within the application zone and such vortices intermittently extend to and past the downstream metering blade of the short dwell coater to form streaks in the resultant coating.
The present invention seeks to overcome the aforementioned problems by providing a short dwell coater which includes a cross-machine directional pipe supplied with coating material and a vane extending from the pipe towards the web for generating a hydrodynamic wedge between the vane and the web.
Accordingly, the present invention provides a short dwell coater apparatus for applying coating to sheet materials and eliminates vortexing in the application zone.
An object of the present invention is the provision of a short dwell coater that overcomes the aforementioned problems of the prior art coaters and which makes a considerable contribution to the art of applying coating material to a moving web.
Another object of the present invention is the provision of a short dwell coater which includes a vane for generating a hydraulic wedge between the vane and the web for reducing entrained air vortices within the application zone.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.